Fracture and R-curve behavior of an intermetallic β-stabilized TiAl alloy with different nearly lamellar microstructures

Abstract Four different microstructures of an engineering multi-phase Ti–43.5Al–4Nb–1Mo–0.1B alloy (in at.%) were fracture mechanically tested under monotonic loading conditions from room temperature up to 700 °C. Monotonic loading crack resistance curves were measured using the potential drop technique and the calculated crack lengths were compared to optically measured crack lengths during in-situ experiments under the light-optical microscope. By examining the fracture surfaces and the polished side faces of the samples in the scanning electron microscope the fracture mechanisms were evaluated. It was found that the fracture toughness mainly depends on structure and phase arrangement at the boundaries and can be enhanced up to 30% by having thick boundary areas with a few micrometers in width, consisting of unconnected β O and γ grains. In contrast, a connected β O -phase at the colony boundaries as well as a texture which provide lamellae parallel to the subsequent fracture surface reduce the fracture toughness.